Robots are used to perform many tasks in the semiconductor industry, such as the automated handling of substrate media or other objects. In the semiconductor industry, typical media and other objects include individual silicon wafers or wafer carriers, flat panel displays, and hard disk media. Robots may be used for handling media in, for example, wafer processing cluster tools, wafer inspection equipment, metrology equipment, and equipment for hard disk thin film deposition, and in transferring media between production equipment and automated material handling systems in semiconductor factories. Robots may be used in both atmospheric and vacuum environments.
One class of robots is known as jointed arm robots or more specifically, jointed cylindrical coordinate robots. Cylindrical coordinate robots include a configuration consisting of an arm having a limb that is movable in a horizontal plane and attached to a revolute joint. The revolute joint is mounted on a carriage to which a reciprocating vertical movement is supplied along an axis of a vertical column. The limb can move in and out in a radial or R-direction. Also, the arm can rotate as one unit on the carriage in the θ-direction. The arm design is based upon a multiple-linked open kinematic chain. This arm configuration is also known as a Selective Compliant Articulated Robot Arm (SCARA) configuration.
In general, the basic components of a robot system are a manipulator, a power conversion module, sensory devices, and a controller. The manipulator consists of links and joints (with included gears, couplings, pulleys, belts, and so on). The manipulator can be described as a system of solid links connected by joints. Together, the links and joints form a kinematic chain. A kinematic pair comprising a joint and an adjacent link may also be called a linkage.
Two types of joints are used in manipulator mechanisms, revolute and prismatic. A revolute, or rotary, joint allows rotation of one link about the joint axis of the preceding link. A prismatic joint allows a translation between the links.
The motion of a joint is accomplished by an actuator mechanism. Motion of a particular joint causes subsequent links attached to it to move with respect to the link containing the joint's actuator. The actuator can be connected to the link directly or through a mechanical transmission when some output characteristics (force, torque, speed, resolution, etc.) of the actuator need to be changed, depending upon the performance required.
The manipulator usually ends with a link that can support a tool. In semiconductor wafer processing equipment, this tool is usually called an end effector. The interface between the last link and the end effector may be called an end effector mounting flange. The links, which are connected through the joints to the actuators, move relative to one another in order to position the end effector in an X-Y-Z coordinate system.
A configuration of a single arm robot or SCARA arm robot that is commercially available has three parallel revolute joints, which allow for the arm's movement and orientation in a plane. Often, the first revolute joint is called the shoulder, the second revolute joint is called the elbow, and the third revolute joint is called the wrist. The fourth, prismatic, joint is used for moving the end effector normal to the plane, in the vertical or Z-direction. Actuators (for example, closed-loop control servomotors) and motion conversion mechanisms are included in the mechanism to enable the motion of the joints. A controlled movement of each link, i.e., the positioning and the orientation of the end effector in the X-Y-θ-Z coordinate system, can be achieved only when an actuator controls each joint of a manipulator. Actuators can control joints directly, or when the reduction in force and torque is required, via a motion conversion mechanism.
For serial kinematic linkages, the number of joints equals the required number of degrees of freedom. Thus, to move and orient the end effector of the single arm per a required set of X-Y-θ-Z coordinates, four joints (three revolute and one prismatic in the vertical direction) are required. In some multiple-linked jointed cylindrical coordinate type robots, end effectors often are required to be oriented such that a center line drawn along the end effector and projected towards the column of the robot always intersects with the axis of revolution of the first rotary joint (the shoulder joint). In this case, the manipulator requires just three degrees of freedom (R-θ-Z). An individual actuator does not control the joint of the end effector, and only three actuators are required.
Known dual arm robots of this type for handling substrate media may include two shoulder joints, two elbow joints, and two wrist joints. The arms can also move vertically a predetermined distance along the translational axis of the prismatic joint of the carriage, which supports the first rotary joint (the shoulder joint of the arm). The individual links of both arms are at the same level and the shoulder joints are next to each other, requiring use of a C-type bracket between one of the arms and its end effector, so that both end effectors can pass each other. This robot, however, cannot be used in a vacuum transport module built per SEMI MESC standards, because the isolation valves of such a vacuum transport module are too narrow to allow passage of the arm that includes the C-type bracket per the SEMI specification that defines wafer transport planes within cassette and process modules. Also, the arms cannot rotate independently in cylindrical coordinates. The angular relationship between the vector of the straight-line radial translation of the individual end effectors of each arm (in robots that are presently available commercially) is permanent and established during the assembly of the robot. Often, the individual arms of the dual arm robot are directed along the same vector.
Generally in substrate processing systems the rotation of arms of transfer robots with multiple arms are linked to one another so as one arm rotates the other arm(s) rotates as well. The end effectors of the transfer robots are generally located in different planes so that a fast swap (e.g. one end effector radially passes over/under the other end effector so that as one substrate is removed from a holding station another substrate is substantially simultaneously placed at the holding station without retraction of the arms to battery) of substrates to and from holding locations generally occurs using either a Z axis capability of the transfer robot or holding station.
It would be advantageous to decouple the rotation of the arms of substrate transfer robots so that each arm is capable of independent operation.